The goals of this proposal are: (1) The isolation of single pieces of DNA from Drosophila melanogaster of molecular weight 10 to the 10th power and greater so the length of the simple satellite sequences in this genome can be determined. Approach to sedimentation equilibrium is being used as a measure of molecular weight. The amount of satellite at each molecular weight determines the length of the satellite sequences. (2) The isolation of a region of the Drosophila melanogaster genome in native form which has been described by Kram, Botchan, and Hearst. The partially melted DNA will be studied in the electron microscope to verify the spacing pattern of simple sequences previously reported. We believe this class of DNA is of fundamental importance for the study of coarse genetic control in the higher organism. (3) The establishment of a similar class of DNA in the mouse genome and the study of the phase relationship between replication of the simple sequence DNA and the transcription of the genes adjacent to it in 3TS (mouse) tissue culture cells. (4) It is not known if the RNA sequences transcribed on the DNA adjacent to the simple sequences are in true messenger RNA's or if they remain in the nucleus. We will, therefore, assay for these RNA sequences by hybridization in polysomes and in nuclear RNA preparations to determine if this RNA which has already been detected ever leaves the cell nucleus.